6.5-stable review patch. If anyone has any objections, please let me know.
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From: Sebastian Andrzej Siewior bigeasy@linutronix.de
[ Upstream commit 41b43b6c6e30a832c790b010a06772e793bca193 ]
It was brought up by Tetsuo that the following sequence:
write_seqlock_irqsave() printk_deferred_enter()
could lead to a deadlock if the lockdep annotation within write_seqlock_irqsave() triggers.
The problem is that the sequence counter is incremented before the lockdep annotation is performed. The lockdep splat would then attempt to invoke printk() but the reader side, of the same seqcount, could have a tty_port::lock acquired waiting for the sequence number to become even again.
The other lockdep annotations come before the actual locking because "we want to see the locking error before it happens". There is no reason why seqcount should be different here.
Do the lockdep annotation first then perform the locking operation (the sequence increment).
Fixes: 1ca7d67cf5d5a ("seqcount: Add lockdep functionality to seqcount/seqlock structures") Reported-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/20230920104627._DTHgPyA@linutronix.de
Closes: https://lore.kernel.org/20230621130641.-5iueY1I@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/seqlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 987a59d977c56..e9bd2f65d7f4e 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -512,8 +512,8 @@ do { \
static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass) { - do_raw_write_seqcount_begin(s); seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); + do_raw_write_seqcount_begin(s); }
/**